Research On Technologies Of Magnetically-Coupled Resonant Wireless Power Transfer For Underwater Vehicles

Underwater Vehicle(UV)is the effective tool for ocean exploration and utilization,which makes it a research focus in the world at present.Energy issue is the main factor restricting the long-term continuous operation of the UV in the ocean environment.Based on the magnetically-coupled resonant wireless power transfer(WPT)technology,the use of a seafloor base station for wireless electric power supply to the UV can increase its concealment and utilization,which has a good application prospect.This thesis focuses on the magnetically-coupled resonant WPT technology.Based on the research of the basic circuit models and the magnetic coupler adapted to the UV and consideration of the particularity of the seawater medium and complexity of the marine environment,the calculation method of the eddy current loss and the system equivalent circuit model in the seawater and the design of the anti-ocean-current WPT system are studied.(1)The basic circuit models and compensation topologies of the magnetically-coupled resonant WPT technology are studied.Based on the equivalent mutual inductance circuit model,the transfer profermance and the short-and open-circuit characteristics of the dual-coupled LCC-S,SS,single-coupled LCC-S and LCC-LCC compensation topologies are analyzed.It is found that the proposed dual-coupled LCC-S topology can keep the output power stable and achieve both short-circuit and open-circuit protection without the complex control method.The SS and LCC-LCC topologies have constant current output and can achieve short-circuit protection without the open-circuit protection ability.The single-coupled LCC-S topology has constant voltage output and can achieve open-circuit protection without the short-circuit protection ability.(2)Four coil structures are proposed for the rotationally symmetric structure of the underwater vehicle.1)An underwater WPT system with a curly coil structure is proposed.Based on the optimization criterion of the minimum weight of the receiver,the unipolar and bipolar curly coils are optimized.It is found that the optimized open angles of both coil structures are 60° and the requirement of the maximum magnetic flux density is satisfied under this case.2)The coil structure of the dual-coupled LCC-S compensation topology is designed.It is found that the system efficiency and output power remain relatively stable when the x-misalignment increases from 0 mm to 90 mm.3)The solenoid coil structure with360° anti-rotational misalignment characteristic is proposed,which can achieve a stable mutual inductance during the rotational misalignment.The finite element analysis(FEA)model is established,with which the self-inductance and mutual inductance are analyzed.It is found that the system efficiency and output power remain relatively stable when the rotational misalignment increases from 0° to 360°.4)To solve the severe changes of the mutual inductance caused by the rotational and axial misalignment at the same time,the three-coil structure with the 360° rotational misalignment tolerance and axial misalignment tolerance is proposed.The FEA model is established,with which the self-inductance and mutual inductance are analyzed.It shows that the mutual inductance can remain stable during axial the misalignment.(3)Based on the Maxwell’s equations,the theoretical calculation model of the eddy current loss generated by the spiral circular coils in the seawater is established,and the calculation equations of the eddy current loss with and without misalignment are derived respectively.Based on the calculation model of the eddy current loss,the equivalent circuit model of the WPT system in the seawater medium is established,with which the optimization method is proposed to optimize the resonant frequency and operating ferquncy.The experimental prototype of the underwater WPT system is set up and experiments are conducted both in the air and seawater.The results show that the optimum resonant frequency in the seawater is lower than that in the air.Morover,the optimum operating frequency in the swater should be larger than the resonant frequency to improve the system efficiency.(4)The spatial electric field distribution of the three-coil structure in the ocean environment is analyzed,with which the analytical expression of the eddy current loss is obtained.Based on the equvailent resistance of the eddy current loss,the equivalent circuit model of the three-coil WPT system in the seawater medium is established,through which the transfer profermance is analyzed.The experimental prototype of the underwater three-coil WPT system is set up and the experimental results show that the efficiency of the three-coil system is higher than that of the two-coil system,and the system efficiency and output power of the three-coil system can remain stable when the axial misalignment increases from-40 mm to 40 mm.In conclusion,this thesis focuses on the circuit model of the WPT system,the magnetic coupler adapted to the UV,the calculation method of the eddy current loss and the system equivalent circuit model in the seawater,and the design of the anti-ocean-current WPT system and the relevant solutions are proposed,which lays the theoretical and technical foundation for the application of the WPT technology in the ocean environment and can solve the energy issue of the long-term continuous operation of the UV.